1. Field of the Invention
The present invention relates to a power supply system, in particular, to a power supply apparatus and a power supply method that each use a high impedance battery used for electric equipment such as a notebook PC (notebook type personal computer).
2. Description of the Related Art
In regard to certain electric equipment, such as a mobile computing apparatus such as a notebook PC, it is strongly desired not only to have a thin and lightweight battery, but it also desired to have an enlarged battery capacity to lengthen the utility of such an apparatus. In such electric equipment, it is commonly known to utilize a secondary battery, such as a nickel-cadmium battery (NiCad battery), that can be charged and recharged many times by repeating the process of charging and discharging. However, recently, lithium ion batteries having high energy density are now being broadly used.
The lithium ion battery is also useable as a secondary battery that is made to have improved safety and to be able to perform repeated charging and discharging. The lithium ion battery has an energy density per unit weight nearly two times as high as that of a NiCad battery and a longer life. In addition, the lithium ion battery has many advantages over NiCad batteries such as, for example, not having a memory effect.
On the other hand, as a secondary battery for electric equipment that is anticipated to be widespread, there exists a lithium polymer battery. A lithium ion battery utilizes liquid electrolyte, but in the lithium polymer battery, a solid resin (polymer) is used, and hence the polymer provides further improved safety features over traditional battery sources and is also relatively thin. This lithium polymer battery is not common yet in terms of electrical characteristics and is also not yet readily available on a mass-production scale. Additionally, the lithium polymer battery has disadvantages that its internal resistance and impedance are relatively high. In a high impedance battery such as this lithium polymer battery, it is possible to have large capacity in the discharging of small current, but in the discharging of the large current, the battery voltage immediately drops to that of the final voltage of discharge. In consequence, for example, even if a lithium polymer battery is adopted in a notebook PC, since the lithium polymer battery has a superior volume capacitance ratio over that of the lithium ion battery, it is not possible to adequately use the capacity present. Thus, it is not possible to make full use of the features of a lithium polymer battery, such as that of the capability of large capacity.
The present invention has been achieved in order to solve such technical issues, and an object of the present invention is to make full use of the features of a battery having large capacity and high impedance.
In addition, another object of the present invention is to utilize a battery for a long period of time by effectively using a high impedance battery having large capacity.
For these objects, the present invention is configured so that a lithium polymer battery is utilized as a battery for electronic equipment, that is, in usual operation, electric power is supplied from the lithium polymer battery to a main body, and when current larger than a certain value is required, a predetermined amount of electric power is supplied from a main battery such as a lithium ion battery. Thus, a power supply apparatus of the present invention is characterized in that the power supply apparatus comprises: a first battery supplying electric power, and a second battery not only supplying electric power but also outputting the electric power in voltage in excess of that of the first battery, and that the power supply apparatus supplies the electric power from the second battery until the load power reaches a predetermined amount, and supplies electric power in excess of that available from the first battery alone when the load power exceeds the predetermined amount by supplying electric power from the first battery and the second battery in combination.
Here, the power supply apparatus can further comprise a current limiting circuit letting the second battery output electric power until load power reaches a predetermined amount and limiting current such that output voltage from the second battery may be dropped when the load power reaches a predetermined amount. Owing to this, it is possible to prevent a high impedance battery, represented by a lithium polymer battery, from discharging in large current, and hence it is possible to avoid the problem of the battery immediately reaching the final voltage of discharge.
In addition, it is preferable from the viewpoint of being able to continue battery operation to make it a feature to completely replace the second battery with the first battery after using up the second battery, and to supply electric power by this first battery. Furthermore, it is possible to suppress heat generation from the battery.
Moreover, a power supply apparatus of the present invention, in a preferred embodiment, comprises: a first battery supplying electric power, a second battery that supplies electric power by being connected to the first battery in parallel, which outputs electric power in voltage higher than the first battery, and is a battery comprised of, for example, a lithium polymer battery having high internal impedance, and a rectifier circuit such as a diode preventing flow of current from the second battery to the first battery. Here, where electric power is supplied from the second battery until the output voltage of the second battery with high internal impedance drops to an output voltage level based on the first battery by the increase of output current, and electric power is supplied by the first battery and the second battery after the output voltage of the second battery dropped to the voltage level based on this first battery, it becomes possible to also supply electric power to the main body whose load becomes high.
Further, it becomes possible by the present invention to deal with the problem where the battery voltage of the second battery with high internal impedance sharply drops and reaches the final voltage of discharge. Here, xe2x80x9cvoltage level based on the first batteryxe2x80x9d is the voltage, which is obtained by subtracting forward voltage in a rectifier circuit, or the like not to be limited to the voltage that is just outputted from the first battery, and means a voltage level corresponding to an output of the second battery when the first battery is connected in parallel.
In addition, the first battery and/or the second battery can be any one of a primary battery that cannot be charged, or a secondary battery that can be charged and discharged.
Additionally, a power supply apparatus of the present invention, in a preferred embodiment, comprises: a first battery and a second battery that supply electric power and can be used many times by repeating charging and discharging; and a current limiting circuit that supplies electric power from the second battery in normal use if a battery with high impedance is connected as the second battery, and that limits an output from the second battery when current exceeding a certain value is required. Here, the current limiting circuit operates with a specific signal where when a lithium polymer battery is connected as the second battery, this current limiting circuit is preferable in terms of being able to drive the current limiting circuit by distinguishing a case that a battery with high impedance is connected.
Further, the power supply apparatus, in a preferred embodiment, provides electric power equal to an amount exceeding an output from the second battery is supplied from the first battery when an output from the second battery is limited by this current limiting circuit.
On the other hand, electric equipment to which the present invention is applied comprises: a main battery supplying electric power to a main body; and a lithium polymer battery supplying electric power by being connected to the main body, and supplying voltage higher than an output voltage range of the main battery, and that the electric equipment supplies electric power from the lithium polymer battery if the load power of the main body is within a predetermined amount, and supplies load power equal to an amount, exceeding a predetermined amount, by the main battery when the load power of the main body exceeds the predetermined amount. By using such a configuration, in general, it is possible to effectively use a lithium polymer battery, which has a large capacity but a high impedance, by making use of its intrinsic characteristics. In particular, this preferred embodiment provides an adequate and efficient use of a lithium polymer battery in electric equipment such a mobile computing apparatus (i.e., a notebook PC) for which thinning is required.
In addition, in order to achieve the objectives of the present invention, the present invention provides an electric power supply method for supplying electric power from a first battery and a second battery with high impedance, wherein the electric power supply method comprises the steps of: outputting the electric power in voltage higher than an output voltage range of the first battery from the second battery; supplying the electric power from the second battery when a necessary current value is not larger than an predetermined amount; and supplying the electric power from the first battery and the second battery when the necessary current value exceeds the predetermined amount. The predetermined amount may be, for example, an allowable current value for making the second battery not reach the final voltage of discharge, or may be defined as a current value when the voltage of the second battery reaches an output voltage range of the first battery due to the voltage drop of the second battery caused by, for example, impedance.
Further, this method may further comprise the further step of performing control lest current larger than a certain amount should be flown from the second battery positively when this load power exceeds this predetermined amount.
In another preferred embodiment, the present invention is an electric power supply method for supplying electric power to electric equipment comprising the steps of: recognizing that a battery with large capacity and high impedance is connected to the electrical equipment; supplying electric power from the battery recognized when load power by the electric equipment is not larger than a predetermined amount; and limiting output current by dropping the output voltage of the battery when the load power by the electric equipment exceeds the predetermined amount. Furthermore, the electric power supply method may further comprise the step of supplying electric power, which is equal to an amount exceeding the electric power of the battery, from another battery when the load power by this electric equipment exceeds a predetermined amount.